1. Field of the Invention
The invention relates to a miniature X-ray source device connected to a distal end of a guiding wire for insertion towards a desired location within an animal body for effecting radiation therapy, said X-ray source device at least comprising a vacuum tube accommodated in said housing containing a cathode and an anode spaced apart at some distance from each other; electron freeing means for freeing electrons from the cathode; electric field means for applying during use a high-voltage electric field between said cathode and said anode for accelerating said free electrons; said vacuum tube being at least partly transparent to X-ray radiation emitted by said anode, as well as cooling means for cooling at least said anode.
The present invention relates to a generation of X-rays for medical purposes, and in particular it relates to miniature X-ray source device for intravascular treatment of lesions in body tissue, in particular for treatment of stenosis in coronary vessels and the treatment of cancer tumours.
2. Description of the Related Art
Radiation therapy is a well-established method for treatment of several diseases, including cancer. The presumptive usefulness of a miniature X-ray source device is clear. The insertion of such a source device into vessels or other body cavities would allow the delivered radiation dose to be confide to a small tissue region. More specific, a catheter with a miniaturized X-ray source device could be used for irradiation of cardiovascular tissue.
A miniature X-ray source device according to the above preamble is for example known from U.S. Pat. No. 6,319,188 B1. In this patent publication an embodiment of an X-ray source device is disclosed, having a cylindrically-shaped vacuum tube, wherein a cathode and an anode spaced apart are accommodated. The anode is mounted on a distal end of said miniature X-ray source device.
The vacuum tube is to be evacuated to a preferred vacuum level required for a proper operation of the miniature X-ray source device. Furthermore, the known miniature X-ray source device is provided with electric field means for establishing a high-voltage electric field between the anode and cathode. Electrons emitted from said cathode are accelerated by said established high-voltage electric field and impact with a high kinetic energy on said anode material. In the anode material X-ray radiation is generated with a high energy level.
As the vacuum tube is entirely highly transparent to X-ray radiation, said generated radiation can leave the vacuum tube towards the patient's tissue in which the X-ray source device is inserted. AS the generated X-ray radiation leaving the miniature X-ray source device exhibits a high energy level, the X-ray radiation is highly suitable for performing radiation therapy in said patient's body, for example for treating cancer tumours.
However, upon impact of the free electrons emitted from the cathode and accelerated towards the anode, only a small amount of the kinetic energy of said electrons is converted into X-ray radiation. A significant large amount is converted into heat significantly increasing the working temperature of the anode. Due to the rather small dimensions of the X-ray source device as well as due to the environment (the patient's body) in which the X-ray source device is used and also in order to extend the life span of the device it is necessary to cool the anode to a proper working temperature.
In U.S. Pat. No. 6,319,188 it is suggested to use an open ended system or a closed loop system comprising a thin sheath of a cooling liquid transported over the cable and X-ray tube. Although with such cooling means a higher rate of heat dissipation and subsequently a decrease in the working temperature of the anode can be obtained they require significant cooling capacity of the cooling means before an efficient cooling of the anode is obtained. Furthermore with a construction like suggested in U.S. Pat. No. 6,319,188 the outer dimensions of the X-ray source device are increased, further limiting the application of such a device in the patient's body.
Furthermore, in the known miniature X-ray source device provided with cooling means an accurate control of the cooling means in order to establish a desired temperature of the anode and thus of the operational conditions of the miniature X-ray source device is not possible.